1. Field of the Invention
The present invention relates to a unit pixel for allocating and storing photoelectrons generated by photoelectric conversion, a solid-state image sensing device having the unit pixel, and a method for summing unit pixel signals.
2. Description of the Related Art
Known conventional applications of image sensors include technologies using a time-of-flight (TOF) method for measuring a distance to a target object in a contactless manner. In one known technology using the TOF method, photoelectrons (negative electric charge) generated in a photoelectric conversion element are allocated and then read out. In Ryohei Miyagawa and Takeo Kanade, “CCD-Based Range-Finding Sensor”, IEEE Transactions on Electron Devices, Vol. 44, No. 10, October 1997, pp. 1648-1652 and Ryohei Miyagawa and Takeo Kanade, ITE Technical, Vol. 19, No. 65, pp. 37-41 (November 1995), a pulsed light is emitted from a light-emitting device in an emission period and is not emitted therefrom in an emission stop period, the light-emitting device is driven to repeat the emission period and the emission stop period with the same time length at a duty ratio of 50%, the pulsed light is detected in synchronism with the periods, and thus generated photoelectrons are distributed in two directions. The distance to the target object is measured using the photoelectrons distributed in the two directions. In addition, in Japanese Laid-Open Patent Publication No. 2010-32425, the photoelectrons generated in the photoelectric conversion element are distributed in four directions.